The present invention relates to a control system for an internal combustion engine, or more in particular to an internal combustion engine control system in which a resistance index (such as an equivalent gradient) specifying the driving force for an operating condition (such as vehicle speed) under a prevailing load condition is calculated, thereby to effect an advance control rapidly responding to a target value for any operating condition.
Control systems for an internal combustion engine so far suggested are configured in such a manner that the state feedback control is effected in accordance with such quantities as the amount of supplied air, the amount of injected fuel, the rotational speed of the engine and the airfuel ratio, thereby to control the generated torque, engine speed and air-fuel ratio to optimum conditions as disclosed in JP-A-61-145339 and JP-A-61-171618.
On the other hand, throttle control system in which such an actuator, operating as a servo motor, is driven in accordance with a command from a control system to control the opening degree of the throttle valve is disclosed in JP-A-59-196937 and JP-A-59-196939.
The control systems for internal combustion engines suggested in the aforementioned Japanese patent publications assume that a dynamic model of an internal combustion engine controlled in a manner to attain an optimum gain by feedback control has a linear characteristic in the vicinity of an operating point, and no consideration is given to possible use of dynamic control to change the engine speed to a great measure, thus making it impossible to effect optimum feedback control over the entire range of operating points.
Also, no concept of advance control has been introduced for removing the transmission delay based on the internal structure or power transmission mechanism of an internal combustion engine, or the time delay before a change in the amount of supplied air or the fuel supply reaches a cylinder or the delay of rise time attributable to the complicated mechanisms. As a result, the problem is posed that it is impossible to dampen the vehicle vibrations caused by sudden changes in the amount of air or fuel supply.
A method of advance control has been suggested by JP-A-61-171618 in which a required drive torque is calculated from the difference between a target vehicle speed and an actual vehicle speed, and a fuel injection amount or a gear ratio is set on the basis of the value thus calculated. In view of the many factors involved in the calculation of the drive torque, however, this conventional system is incapable of accurate calculation of the required drive torque, and the amount of fuel injection or the gear ratio cannot be set under other than predetermined conditions.